<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8" />
	<title>圆</title>
</head>
<body>
	<input type="" name="" id="a" value="" placeholder="半径"/>
	<input type="" name="" id="b" value="" placeholder="周长"/>
	<input type="" name="" id="d" value="" placeholder="面积"/>
	
	<script type="text/javascript">
		
		var  r = prompt("请输入圆的半径");
		 a.value=r; 	
		var p = 3.14;
		
		document.querySelector('#a');
		document.querySelector('#b');
		document.querySelector('#d');
		
		
//		圆的周长
		var l = 2*p*r;
		b.value=l;
		
		
//		圆的面积
		var s = p*r*r;
		d.value=s;
		
		
		
	</script>
</body>
</html>